1. Field of the Invention
The present invention relates generally to reed switches and more specifically to the method of using one or more reed switches to control one or more devices.
2. Description of the Related Art
Reed switches are magnetically-operated switches, which are typically formed by a pair of spaced ferromagnetic contacts or blades, hermetically sealed in a glass capsule. In a typical application and use of a reed switch, the blades are connected to outside leads—each outside lead being part of a circuit. The exposure of the blades to a magnetic field—coming from either a permanent magnetic or electromagnetic generation—forces the blades to move, either contacting one another or moving away from one another. The contacts or blades may be normally-open or normally-closed. As used herein, in a normally-closed reed switch, the blades normally are not contacting each other but will close or contact each other when a magnetic field is present. In a normally-open reed switch, the blades normally contact each other but will open or separate when a magnetic field is present. Upon removal or shielding of the magnetic field from the reed switch, the blades of the normally-closed reed switch will separate or open whereas the blades of the normally-open reed switch will close or contact each other.
Generally, the reed switch is activated (that is, causing the ferromagnetic blade to move, be it closing the circuit or opening the circuit) via the use of a magnetic field. Such an activation allows communication to be established with a system or device. In some instances the communication may be the lack of a signal or electrical energy being returned when the reed switch opens the circuit, while in other instances, the communication may be the circuit being completed.
One recognized use of a reed switch is monitoring the “change of state” of something, for example a door or window, in security or burglar alarm systems. In such an example, a reed switch causes a circuit to be completed (i.e., closed) or broken (i.e., opened) when a window or door opens or closes. Typically, this change of condition (the opening or closing of the circuit) is automatically detected by a central alarm system or the like, indicating whether or not an unauthorized “change of state” has occurred. A typical security use of such a reed switch may be, for example, on a window or door assembly of a house or on a roll-up door assembly of a storage shed. In such situations, it is well known and understood that the central alarm system typically receives a low voltage signal passing through the reed switch to indicate one status of the door or window, and does not receive the low voltage signal from the open reed switch when the door or window is in another state.
With the use of reed switches to control a device, several design considerations must be taken into account. Reed switches are by their very nature fragile—that is, the glass capsules can break. An exacerbation of the fragile nature is the likelihood that two reed switches in too close proximity to one another may hit and break each other.
Biasing a Reed Switch.
It has been known for many years by those skilled in the art that biasing a reed switch with a first stationary magnet may have a benefit in some instances. One such application of biasing a reed switch is seen in U.S. Pat. No. 2,877,361 to Chase, issued Mar. 10, 1959. The Chase patent teaches using the magnetic flux of a stationary biasing magnet next to a set of reed switch contacts of a stationary reed switch to bias the set of reed switch contacts to the “magnet present” closed state. The closed state remains until the magnetic flux of a second moving magnet or actuator magnet, attached to a movable part of an opening, is present to cancel or annul the flux field of the stationary biasing magnet away from the biased reed switch contacts. This results in the reed switch contacts changing to the “magnet not present” open state even though the biasing magnet has not moved from its stationary position next to the reed switch contacts.
Thus, biasing a stationary set of reed switch contacts with an adjacent small stationary biasing magnet, having a small magnetic flux field just strong enough to bias the set of reed switch contacts to the “magnet present state,” in conjunction with a second larger magnet with a stronger magnetic flux field spaced farther away from the set of reed switch contacts is known in the prior art. When the presence of the second larger magnet's magnetic field is present on the reed switch contacts, the second larger magnet overpowers the smaller first stationary biasing magnet and the contacts change to their “magnet not present” state even though magnets are present. The second larger magnetic flux presence could be physically moved away from the set of reed switch contacts and the first stationary biasing magnet to remove the second larger magnetic flux presence from the set of reed switch contacts and biasing magnet. Alternatively, the second larger magnet could also be stationary and ferromagnetic material moved between the set of magnetically biased reed switch contacts and the second larger stationary magnet removes the second larger magnetic flux from the magnetically biased reed switch contacts to change the state of the reed switch. It is further known that a reed switch apparatus can have more than one set of reed switch contacts pre-biased by a biasing magnet.
Another technique of using a stationary biasing magnet to influence a set of reed switch contacts is taught in U.S. Pat. No. 4,943,791 to Holce et al., issued Jul. 24, 1990. A first stationary biasing magnet placed to one end of a set of reed switch contacts provides a portion of the required magnetic flux density to cause magnetic actuation or the “magnet present” state, but not enough. The remaining portion of magnetic flux density required to change the state of the reed switch contacts to the “magnet present” state is provided by a second moving magnet. By using a first stationary biasing magnet in this arrangement the reed switch contacts require less of a magnetic flux from the second moving magnet, creating a greater actuation distance to change to the “magnet present” state by the second moving magnet, resulting in a wide gap switch.
By influencing a set of reed switch contacts with a biasing magnet has shown to facilitate a certain balance between the magnetic fields of all used magnets within the equation. This balance is short lived due to constantly changing variables within the equation. The magnets, for example, lose some of their magnetic flux properties over time, resulting in inconsistent results. This inconsistency is even more evident when using not only a fixed biasing magnet, but also a fixed stationary activation magnet and controlling the magnetic field with a piece of ferromagnetic material between the fixed stationary actuation magnet and the set of reed switch contacts being biased by the fixed biasing magnet. Any inconsistency can be overcome by correctly matching all the magnets' magnetic flux properties within the equation to include a large demagnification error window graduated over time to provide a more consistent result.
Various Magnetic Reed Switch Configurations.
As discussed above, a simple reed switch configuration is generally formed by one set of contacts that are part of the flexible blades within the sealed glass bulb of a reed. Other more complex configurations having more than one set of contacts exist, such as a single pole double throw switch. Following are some different combinations and configurations of magnetic reed switches illustrated schematically in FIGS. 20A-E:
Normally Open Single Pole Single Throw Switch (N.O. SPST) (FIG. 20A);
Normally Closed Single Pole Single Throw Switch (N.C. SPST) (FIG. 20B);
Normally Open/Normally Closed Single Pole Double Throw Switch (N.O./N.C. SPDT) (FIG. 20C);
Normally Open Double Pole Single Throw Switch (N.O. DPST) (FIG. 20D); and
Normally Closed Double Pole Single Throw Switch (N.C. DPST) (FIG. 20E).
Magnetic reed switches, like mechanical switches and solid state switches, utilize some sort of formed open or closed contacts in different configuration combinations held within the switch. As described above, reed switch contacts are typically encased within a sealed glass bulb filled with either a gas or vacuum-packed and typically at a different pressure than earth's atmospheric pressure to preserve the contacts from the environment. Mechanical or solid state switches may or may not be sealed in some fashion, but do employ all the contact combinations and configurations of a reed switch.
A magnetic reed switch requires some sort of magnetic flux exposed upon the reed switch for the reed switch to change state. A mechanical or solid state switch usually requires some sort of moving mechanical interaction to change state. Some forms of a solid state switch also require power in order to change states.
Transportable Storage Containers.
In recent years the transportable storage container industry for individual and company rental applications has grown significantly. Typically, the renter contacts the storage container company, and has a portable self-storage container delivered to the renter's location from the storage company's warehouse or holding location. The renter fills the portable container with the renter's contents. Typically, the portable container may be at the renter's location from one day to several months, during which time the portable container has no alarm and is vulnerable to thieves and/or terrorists. The portable container may be used for temporary, semi-permanent or permanent storage at the renter's location. When the container is no longer needed, it is picked up empty and returned to the storage container company's warehouse or holding area.
In other instances, after the portable storage container is filled with the renter's contents, the storage company is called to pick up the filled container and transport it to the storage company's warehouse or holding area where containers are typically stacked in multiple rows in a very large area. The containers that are filled with items do not have any type of onboard security system or location device to protect the goods inside the containers.
It would be desirable to be able to easily locate a needed specific container out of rows of hundreds of stacked transportable storage containers that all look similar at the warehouse or holding area.
A problem that exists with transportable storage containers is that the portable container's openings are not protected by a security system and the container's contents are unsecured during transportation to and from the renter's location and the entire time the container is at the renter's location, whether it is used for temporary or permanent storage. The only item that typically secures the contents of the container is some type of mechanical lock, which can be physically bypassed without anyone noticing the unauthorized intrusion.
Internal lighting would also be desirable for containers that do not get adequate light when the door is open. Moreover, internal lighting would be beneficial when there is no projected sun light, such as between sunset and sun rise. In certain instances, it would be desirable to be able to automatically control a refrigeration system housed as part of the transportable storage container depending on the condition of the container's openings.